EP1343341A1 - Setting up an emergency connection in a cellular radio communications system - Google Patents

Abstract

The method involves initiating an emergency call with the aid of signaling information from a subscriber station, which is transmitted with the information that is used to establish a channel-switched connection between the subscriber station and the base station. The signaling information is logically associated with radio resource control function. AN Independent claim is also included for the following: a radio communications system of cellular construction.

Description

The invention relates to a method for establishing an emergency call connection in a cellular radio communication system according to the preamble of claim 1.

The invention further relates to a radio communication system according to the preamble of claim 10.

In radio communication systems, information (for example voice, image information or other data) is transmitted with the aid of electromagnetic waves via a radio interface between a base station and a subscriber station - possibly a mobile station. The electromagnetic waves are emitted at carrier frequencies that lie in the frequency band provided for the respective system. With the GSM (Global System for Mobile Communication) - a second generation system - the carrier frequencies are in the range of 900, 1800 and 1900 MHz. For future mobile radio systems with in particular TD / CDMA transmission methods or FD / CDMA transmission methods via the radio interface, such as the UMTS (Universal Mobile Telecommunication System) or other third generation systems, frequencies in the frequency band of approx. 2000 MHz are provided.

Modern radio communication systems, in addition to many other services, should also enable the establishment of an emergency call transmission. Such an emergency call is usually initiated by a subscriber station, in particular also by a mobile subscriber station. Naturally, emergency calls should be identified as such and processed as quickly as possible by the network.

In radio communication connections of the second and / or third generation, information can be transmitted channel-switched (CS circuit switched) or packet switched (PS packet switched).

The UTRAN (UMTS Terrestrial Radio Access Network) consists of a number of radio subsystems (RNS Radio Network Subsystem), each of which is connected to the core network (CN Core Network) via the I _u interface. With regard to channel-switched transmissions and packet-switched transmissions, the I _u interface between the core network and UTRAN is logically divided into the I _u CS and the I _U PS.

In the GERAN system (GSM EDGE Radio Access Network, where EDGE stands for Enhanced Data Rates For GSM Evolution) there is the base station subsystem (BSS Base Station Subsystem) between the fixed network of the GSM network, plus the components base station (BTS Base Transceiver Station) and base station control (BSC Base Station Controller), connected via the A interface to mobile switching centers (MSC Mobile Services Switching Center).

Situations are conceivable in which radio communication systems of the type mentioned cannot serve an emergency call initiated by the subscriber station. Such cases can occur, for example, if there is a temporary interruption in the I _u -CS or A interface. This means that there is sometimes no connection to the channel-switched domain (CSD circuit switched domain), which is necessary, however, since the emergency calls are processed there.

In addition to a temporary interruption of the connections mentioned, there may also be a permanent interruption.

In these cases, the radio network access node (RAN Radio Access Network Node) - be it in the UMTS system (RNC Radio Network Controller) or be it in the GSM system (BSC Base Station Controller) - is informed of the interruption of the interface.

However, there are a number of cases in which the radio resource control functions (RRC Radio Resource Control) in the radio network access node do not notice the existence of an initiated emergency call because this is handled by the NAS signaling (NAS Non Access Stratum). Therefore, the radio resource control cannot take suitable measures to inform the subscriber station that initiating the emergency call is useless in a radio cell in which the NAS signaling connection to the channel-switched domain (CSD) cannot be established. As a result, there is a significant delay for the emergency call or it is even made impossible.

The radio resource control function (RRC Radio Resource Control) is a layer 3 function according to the ISO / OSI layer model, which was created for extensive standardization of communication systems. This network layer (network layer) is responsible for setting up, operating and triggering network connections between open systems. This includes, in particular, the routing and interpretation of addresses, the optimal routing when establishing a connection or during the connection.

If the subscriber station in the UMTS or GERAN system is in a state without a communication connection (idle mode), an emergency call can usually be established by setting up an RRC function connection.

However, this possibility does not exist if the above-mentioned temporary or permanent interruption, for example of the I _u interface connection, exists. In this case, RRC information regarding some frequencies can be transmitted to the subscriber station.

If the subscriber station in the UMTS or GERAN system is in the state of a communication connection (Connected Mode), there is no possibility on the part of the radio resource control to recognize the emergency request, since in the radio cell update messages what information transmissions in the up direction (UP Uplink) in initiate the status CELL_PCH and URA_PCH, an emergency call is not considered. In addition, there is no indication of an emergency call in the direct connection setup message (Initial Direct Transfer Message), which is used to set up a signaling connection to the channel-switched domain (CSD circuit switched domain).

Radio cell reselection is only carried out in the radio communication system on the basis of radio criteria, so that the subscriber station cannot access another radio cell for the emergency call.

In the case of an existing RRC connection, there is no possibility to switch to connection-free mode (idle mode).

Particularly in the case of a packet-switched transmission, the establishment of an emergency call connection upon an emergency call initiation is not secured or even impossible.

Overall, it can be seen that the quick and secure establishment of an emergency call connection is by no means guaranteed.

The invention is therefore based on the object of demonstrating a method and a radio communication system of the type mentioned at the outset which avoid the disadvantages described and improve the situation of the establishment of an emergency call. In particular, network-side detection of an emergency request should be ensured. In addition, it should also be possible to respond to an emergency call in the cases described above.

This object is achieved for the method by the subject described in claim 1.

Advantageous refinements and developments are the subject of the dependent claims.

According to the invention, an emergency call is initiated by the subscriber station with the aid of signaling information, which is transmitted with the information which is used to establish a connection between a channel-switched connection between the subscriber station and the base station.

This signaling information should always be transmitted when an emergency call is initiated, regardless of whether the subscriber station is holding a channel-switched connection or a packet-switched transmission or whether there is no connection (idle mode).

In particular, the signaling information is logically assigned to the radio resource control function, so that it can be ensured on the network side that the radio resource control recognizes the desire to establish an emergency call connection and can react accordingly.

A great advantage of the invention lies in the fact that not only is the problem set solved, but also that this happens and at the same time the system architecture principles are not violated. This would be the case, for example, if NAS information was read in the radio resource controller. An indication of an emergency call in the RRC Initial Direct Transfer Message would violate the system architecture principles.

In one embodiment of the invention, a response message is transmitted from the at least one base station assigned to a radio cell to the subscriber station, on the basis of which the base station is informed that the at least one radio network control device is aware that the subscriber station is requesting an emergency call connection.

In a further development of the invention, the response message from the at least one base station to the subscriber station can be used to inform the subscriber station if at least currently no radio resources for the emergency call connection are and / or have been allocated to the subscriber station. This response message could then be referred to as an _" RRC Initial Direct Transfer Reject Message", for example. Advantageously, the response message is transmitted to the subscriber station immediately after receiving the signaling information relating to the desired emergency call.

The response message can advantageously include information about at least one second cell of the radio communication system in which the subscriber station has radio resources available for transmitting the emergency call. This measure can contribute to the speed of establishing the emergency call connection.

In particular, the response message can include information about cell parameters of the second cell or further cells of the radio communication system. This information may include frequency information, radio cell identification information (Cell ID), radio channel information and / or any other radio cell information.

In response to the response message, the subscriber station can change to a basic state without a communication link (idle mode). The subscriber station can, for example, indicate a release of all signaling connections in response to the response message, so that after all RRC connections have been released, the subscriber station goes into the connection-free basic state (idle mode). There is then the possibility that the subscriber station again sends signaling information for establishing a connection between a channel-switched connection between the subscriber station and a base station.

A radio cell change of the subscriber station can take place in response to the response message. For example, a cell reselection of the subscriber station can be provided (eg in CELL_PCH, URA_PCH, CELL_FACH) and then the subscriber station tries again to initiate an emergency call.

The subscriber station (e.g. in status CELL_DCH) can also evaluate the response message as a handover message. In this case, the response message can also contain more information about the channels used, so that existing packet-switched services can even be maintained.

The radio communication system relating to the invention with a cellular structure comprises at least one subscriber station and at least one base station which is connected via a radio network access node to at least one radio network control device of a radio communication network. According to the invention, means are available for initiating an emergency call from the subscriber station with the aid of signaling information which is transmitted with the information which is used to set up a channel-switched connection between the subscriber station and the base station.

The radio communication system according to the invention can be used to carry out the method according to the invention.

In an embodiment of the invention, means for transmitting a response message, by means of which the base station is informed that the at least one radio network control device is aware that the at least one subscriber station wants to make an emergency call, are in the radio communication system from the at least one base station assigned to a radio cell to the subscriber station intended.

Claims (11)

Method for establishing an emergency call connection in a cellular radio communication system with at least one subscriber station and at least one base station, which is connected via a radio network access node to at least one radio network control device of a radio communication network,
characterized,
that an emergency call is initiated with the aid of signaling information from the subscriber station, which is transmitted with the information which is used to establish a connection between a channel-switched connection between the subscriber station and the base station. A method according to claim 1, characterized in that the signaling information is logically assigned to the radio resource control function. Method according to Claim 1 or 2, characterized in that a response message is transmitted from the at least one base station assigned to a radio cell to the subscriber station, on the basis of which the base station is informed that the at least one radio network control device is aware that the subscriber station is requesting an emergency call connection. A method according to claim 3, characterized in that on the basis of the response message from the at least one base station to the subscriber station, the subscriber station is informed if the subscriber station is and / or has not been allocated radio resources for the emergency call connection at least currently in the radio cell. Method according to claim 3 or 4, characterized in that the response message comprises information about at least one second cell of the radio communication system in which the subscriber station has radio resources available for transmitting the emergency call. A method according to claim 5, characterized in that the response message comprises information about cell parameters of the second cell of the radio communication system. Method according to one of Claims 3 to 6, characterized in that the subscriber station changes to a basic state in response to the response message without the presence of a communication link. Method according to one of claims 3 to 7, characterized in that a radio cell change of the subscriber station takes place in response to the response message. Method according to claim 7 or 8, characterized in that the subscriber station again sends signaling information for establishing a connection between a channel-switched connection between the subscriber station and at least one base station. Radio communication system with a cellular structure comprising at least one subscriber station and at least one base station, which is connected to at least one radio network control device of a radio communication network via a radio network access node,
characterized,
that means for initiating an emergency call from the subscriber station with the aid of signaling information which is transmitted with the information which is used to establish a connection to a channel Connection between the subscriber station and the base station is used. Radio communication system according to claim 10, characterized in that means for transmitting a response message, by means of which the base station is informed that the at least one radio network control device is aware that the subscriber station is requesting an emergency call connection, are provided by the at least one base station assigned to a radio cell to the subscriber station are.